1. Field of the Invention
This invention relates to a process for manufacturing aromatic polyesters, and more particularly, to an improvement in the interfacial polymerization process for manufacturing aromatic polyesters.
2. Description of the Prior Art
A number of processes, such as interfacial, solution or melt polymerization, are known for the manufacture of aromatic polyesters. Japanese Patent Publication No. 1959/1965 discloses an interfacial polymerization process in which aromatic dicarboxylic acid chlorides dissolved in an organic solvent which is incompatible with water are mixed with bisphenols dissolved in an aqueous alkali solution. Japanese Patent Publication No. 5599/1962 discloses a solution polymerization process which comprises reacting aromatic dicarboxylic acid chlorides and bisphenols in an organic solvent. Japanese Patent Publications Nos. 15247/1963 and 28119/1968 disclose a melt polymerization process which comprises heating phenyl esters of aromatic dicarboxylic acids and bisphenols together. The aromatic polyesters prepared by these processes have outstanding heat resistance, and mechanical and electrical properties, and are useful for a wide range of applications, including the manufacture of molded products, films and fibers.
According to the known interfacial polymerization process, a solution of an aromatic dicarboxylic acid chloride in an organic solvent incompatible with water, and a solution of a bisphenol in an aqueous alkali solution are mixed together under intensive agitation. A product having a high degree of polymerization can be obtained if a quaternary ammonium or phosphonium salt is used as a catalyst. If the agitation is discontinued, the reaction product is usually separated into an aqueous solution phase containing inorganic salts, and a cloudy or opaque organic solvent phase consisting mainly of a polymer, but the organic solvent phase contains water in the form of an emulsion. There are even some cases in which no phase separation occurs. It is, therefore, necessary to seperate a lot of water from the polymer. In order to overcome these disadvantages, it has been proposed to adjust the pH value of the aqueous phase to at least 12 and heat it to destroy the emulsion (Japanese Patent Publication No. 2679/1978), treat the reaction product with an aqueous solution containing a lower aliphatic alcohol which is soluble in acetone or water (Japanese Patent Publication No. 12133/1980), use a centrifugal separator (Japanese Laid-Open Patent Specification No. 55286/1973), or employ specific agitating conditions (Japanese Patent Publication No. 41249/1980). The invetors of this invention have found it possible to overcome the disadvantages if a catalyst composed of a specific compound, i.e., an oil-soluble phase transfer catalyst, is employed.